theyre just scripted registrations.
I wrote a plugin that I had intended to morph into doing more, and stopped working on. The other day, I found a plugin that did exactly what I had wanted mine to do.
=== TTC User Registration Bot Detector ===
Contributors: Linda MacPhee-Cobb
Tags: bot, bots, user, registration, block
Requires at least: 2.5
Tested up to: 2.5.1
Stable tag: 1.5
This plugin blocks and logs most bot user registrations.
== Description ==
This plugin automatically bounces most bot attempts at user registration on your blog. You can also blacklist ips and email addresses to block. If an attempt is made to register by a bot that is not blacklisted that email address and ip number are automatically added to the blacklist.
This plugin creates a page under 'Manage'. On it you can blacklist ip numbers, email addresses, domains and extensions you do not want to register on your site.
The management page will also give you a list of all attempts at registration and if they were bounced and why.
You can grab it here:
http://wordpress.org/extend/plugins/ttc-user-registration-bot-detector/
It uses the API from http://www.stopforumspam.com